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2004ApJ...608..781D - Astrophys. J., 608, 781-796 (2004/June-3)

A deep Chandra X-ray observation of the rich young cluster NGC 6530. I. The X-ray source catalog and the cluster population.


Abstract (from CDS):

In a deep 60 ks Chandra ACIS X-ray observation of the very young cluster NGC 6530, we detect 884 X-ray point sources and argue that a very large fraction of them (90%-95%) must be pre-main-sequence (PMS) cluster members, mostly of low masses. This is a significant enlargement of the known NGC 6530 stellar population with respect to previous optical studies, including Hα surveys. We identify 220 X-ray sources with cataloged stars down to V=17, while most unidentified sources have fainter counterparts. Moreover, we find an infrared counterpart in the 2MASS catalog for 731 X-ray sources. The optically identified cluster X-ray sources are found in a band in the H-R diagram above the main sequence, in the locus of 0.5-1.5 Myr PMS stars, with masses down to 0.5-1.5 M. We find evidence of an age gradient across the field from northwest to south, suggesting a sequence of star formation events qualitatively similar to that found in earlier studies of the same region, but differing in the details. A group of X-ray sources showing frequent flares may be associated with the youngest stars in the cluster, suggesting that X-ray flaring activity is especially intense in the youngest PMS phases of low-mass stars.

Abstract Copyright:

Journal keyword(s): Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 6530 - Stars: Coronae - Stars: Pre-Main-Sequence - X-Rays: Stars

VizieR on-line data: <Available at CDS (J/ApJ/608/781): table1.dat>

Nomenclature: Table 1: [DFM2004] NNN (Nos 1-884).

Simbad objects: 896

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